A support structure for a filter element is known from U.S. Pat. No. 5,783,067, for example. The known support structure forms the wall of a support tube, which encloses the outer surface of a filter medium, and which has a pattern of holes that form fluid passage openings. The fluid passages in the support tube are formed as rounded oblong holes, each of which has two side lines that extend parallel to one another, and two curved lines that connect the side lines to one another. The fluid passage openings, which are formed as oblong holes, are aligned in such a way that they each extend in a radial direction along the support tube.
Good operating behavior of the filtering elements used is paramount for the operation of filtering devices, such as those used in hydraulic systems for the filtration of hydraulic fluids, or in other systems for the filtration of fuels, lubricants or other operating resources. The main considerations here are a self-supporting support of the filter media against flow forces acting thereon, which requires a high degree of mechanical strength in the respective support structure. Also, a minimum level of flow resistance should be generated by the support structure. In order to cope with these conflicting demands as much as possible, the prior art forms hole patterns having round holes. In order to achieve the desired low values in the flow resistance, the holes must be disposed such that they are densely packed. Material supports formed between the holes then form weak points in the support structure, making achieving an optimum compromise, as a rule, of structural performance and fluid permeability impossible.